Grey's Anatomy Season 5 Episode 17
I Will Follow You Into the Dark
Derek decides to quit after learning that more of his patients have died than survived; Izzie's interns make an unsettling discovery about "Patient X."
Guest Stars
Jessica Capshaw
Arizona Robbins
Loretta Devine
Adele Webber
Gloria Garayua
Intern Graciella
Mark Saul
Steve
Wendy Hoopes
Tricia Shelley